Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$244.90	3.508%	$253.4911	$253.49	$253.50	$253.50
Purchase #2	$78.33	12.749%	$88.3163	$88.32	$88.30	$88.30
Purchase #3	$187.44	4.648%	$196.1522	$196.15	$196.15	$196.20
Purchase #4	$164.73	3.688%	$170.8052	$170.81	$170.80	$170.80
Purchase #5	$114.26	12.715%	$128.7882	$128.79	$128.80	$128.80
Purchase #6	$69.62	3.387%	$71.978	$71.98	$72.00	$72.00
Purchase #7	$83.29	3.182%	$85.9403	$85.94	$85.95	$85.90
7 purchase totals =	$942.57		$995.4713	$995.48	$995.50	$995.50